Re: Bug in git archive + .gitattributes + relative path

From: René Scharfe <l.s.r@web.de>
Date: Mar 5, 2023, 09:32 UTC
Message-ID: <c91db499-fa26-b902-3ab8-14c52959482f@web.de>
In-Reply-To: <566c2d09-5e18-49c9-fc7c-7b92d1d7c198@mpsd.mpg.de>

Am 04.03.23 um 16:11 schrieb Cristian Le:

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> I should have explained more thoroughly, I have tried to work around
> by doing a `git archive` and then extracting and re-compressing after
> fixing the paths, but this does not preserve the owner and timestamp
> of the original `git archive`, nor can I use the current
> implementation of their tar fixer to correct these since the headers
> are different. I do not have enough expertise to know what headers
> need to be set, how to set the timestamps and so on.

GNU tar has the options --owner, --group and --mtime that allow you to specify arbitrary values for these fields when archiving, no header tinkering needed. That said, tarring with git archive, untarring and retarring with GNU tar is overly complicated and horrible when git archive can do the whole job itself.

> I don't know if the `gzip -n -c` could do a better job at that,

That just compresses tar files to tgz (or tar.gz) format and does not affect any tar headers.

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> but we would still
> not be able to use it as is because we would want the correctly
> generate `export-subst` files, for example for a project built with
> `setuptools_scm` that injects the version of the python package from
> the last tag:
>
> https://github.com/pypa/setuptools_scm#git-archives

Note that git archive allows injecting extra files with the options
 --add-file and --add-virtual-file.  Could that feature perhaps be used
instead of export-subst?

>> There it was introduced along with a script that changes the mtime
>> of archive entries from the current time to the commit timestamp by
>> https://github.com/spacewalkproject/spacewalk/commit/34267e39d472.
> Thanks for pointing me to this. From your understanding, if we only use the git commit directly, we would in principle not need the whole tar fixer (https://github.com/rpm-software-management/tito/blob/91ef962220ec5154722760dbbd982bed032ee484/src/tito/tar.py#L28-L60 and https://github.com/rpm-software-management/tito/blob/91ef962220ec5154722760dbbd982bed032ee484/src/tito/common.py#L871-L890)? If there is no crucial information in the header that is different between the `git archive` and the `tar`/`gzip` with appropriate `mtime`, `mode` and maybe others, maybe there is some hope in fixing this locally.

The tar fixer was rewritten in Python in the meantime and I didn't look it it closely, but if it only sets the mtime of all archive entries to the commit date then it's not needed when giving git archive a commit or tag instead of a tree.

> I'll be looking forward to `--strip-components`, but just to confirm
> my reading of the email, the intent is to have it working with
> `export-subst` right?

That option would work the same regardless whether git archive is given a tree, commit or tag, and it doesn't care about attributes or file contents. It would be especially helpful when giving a commit or tag and a pathspec, and export-subst needs a commit or tag. So in short: Yes. :)

René